<i>Francisella tularensis</i>Type A Strains Cause the Rapid Encystment of<i>Acanthamoeba castellanii</i>and Survive in Amoebal Cysts for Three Weeks Postinfection

El-Etr, Sahar H.; Margolis, Jeffrey J.; Monack, Denise M.; Robison, Richard A.; Cohen, Marissa N.; Moore, Emily; Rasley, Amy

doi:10.1128/aem.01829-09

Cited by 94 publications

(101 citation statements)

References 52 publications

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“…Despite the similarities in co-culture conditions evaluated and the rigorous testing of numerous Francisella and FLA strains in this study, amplification of each Francisella spp. strain in the presence of FLA was not observed (Figures 1-3), which is contrary to the previous studies reporting increases in Francisella CFU densities following co-culture with FLA [33][34][35][36]. Specifically, 3−4 log 10 CFU mL −1 increases of LVS and Fn were observed by days 6−15 in the presence of Ac30010, Ac30234, and Vv at 25−30°C incubation and MOI of 10 [33,35,36].…”

Section: Discussioncontrasting

confidence: 54%

“…However, in all of those studies, the assay buffer used was ATCC 712 medium, or peptone yeast extract (PYG) broth, which is the nutrient rich growth medium for propagation of Ap, Ac30010, and Ac30234 cells. El-Etr et al [34] demonstrated that PYG broth alone supported LVS and Fn U112 growth; thus, amplification of LVS and Fn observed in the previous reports may not have been solely FLA mediated. The AB, used in this study, was shown not to support Francisella growth (Figures 1-3), which eliminated the possibility of false positives, i.e., detection of non-FLA mediated Francisella amplification.…”

Section: Discussionmentioning

confidence: 81%

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Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

Buse

Schaefer

Rice

2016

Acta Microbiologica et Immunologica Hungarica

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Transmission of Francisella tularensis, the etiologic agent of tularemia, has been associated with various water sources. Survival of many waterborne pathogens within free-living amoeba (FLA) is well documented; however, the role of amoebae in the environmental persistence of F. tularensis is unclear. In this study, axenic FLA cultures of Acanthamoeba castellanii, Acanthamoeba polyphaga, and Vermamoeba vermiformis were each inoculated with virulent strains of F. tularensis (Types A and B), the attenuated live vaccine strain, and Francisella novicida. Experimental parameters included low and high multiplicity of infection and incubation temperatures of 25 and 30°C for 0-10 days. Francisella spp. survival was enhanced by the presence of FLA; however, bacterial growth and protozoa infectivity were not observed. In contrast, coinfections of A. polyphaga and Legionella pneumophila, used as an amoeba pathogen control, resulted in bacterial proliferation, cytopathic effects, and amoebal lysis. Collectively, even though short-term incubation with FLA was beneficial, the long-term effects on Francisella survival are unknown, especially given the expenditure of available amoebal derived nutrients and the fastidious nature of Francisella spp. These factors have clear implications for the role of FLA in Francisella environmental persistence.

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Section: Discussioncontrasting

confidence: 54%

Section: Discussionmentioning

confidence: 81%

Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

Buse

Schaefer

Rice

2016

Acta Microbiologica et Immunologica Hungarica

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“…Identification of REP Proteins-F. tularensis proteins were identified from bacteria-amoeba coculture subfractions, as described previously (21). Briefly, subfractions found to induce the highest levels of REP were trypsin-digested using standard methods and were analyzed commercially by ProtTech, Inc. (Norristown, PA) using liquid chromatography tandem mass spectrometry (LC-MS-MS).…”

Section: Methodsmentioning

confidence: 99%

“…We recently demonstrated that fully virulent F. tularensis isolates infect A. castellanii by inducing the amoebae to rapidly encyst (21). The study identified seven putatively secreted F. tularensis proteins that may be responsible for this rapid encystment phenotype (REP) in amoeba, a phenomenon required for long term survival of F. tularensis in these hosts.…”

mentioning

confidence: 99%

“…The study identified seven putatively secreted F. tularensis proteins that may be responsible for this rapid encystment phenotype (REP) in amoeba, a phenomenon required for long term survival of F. tularensis in these hosts. Interestingly, two of the genes encoding these REP proteins are deleted in LVS, consistent with the inability of LVS to induce amoeba encystment (21) and with its attenuated infectivity toward macrophages (1). Here, we focus on the gene product of FTN_0149 from F. tularensis subspecies novicida U112 (NOV), a REP protein with a molecular mass of 34 kDa (REP34).…”

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confidence: 99%

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Structure and Function of REP34 Implicates Carboxypeptidase Activity in Francisella tularensis Host Cell Invasion

Feld¹,

El-Etr²,

Corzett³

et al. 2014

Journal of Biological Chemistry

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Francisella tularensis is the etiological agent of tularemia, or rabbit fever. Although F. tularensis is a recognized biothreat agent with broad and expanding geographical range, its mechanism of infection and environmental persistence remain poorly understood. Previously, we identified seven F. tularensis proteins that induce a rapid encystment phenotype (REP) in the free-living amoeba, Acanthamoeba castellanii. Encystment is essential to the pathogen's long term intracellular survival in the amoeba. Here, we characterize the cellular and molecular function of REP34, a REP protein with a mass of 34 kDa. A REP34 knock-out strain of F. tularensis has a reduced ability to both induce encystment in A. castellanii and invade human macrophages. We determined the crystal structure of REP34 to 2.05-Å resolution and demonstrate robust carboxypeptidase B-like activity for the enzyme. REP34 is a zinc-containing monomeric protein with close structural homology to the metallocarboxypeptidase family of peptidases. REP34 possesses a novel topology and substrate binding pocket that deviates from the canonical funnelin structure of carboxypeptidases, putatively resulting in a catalytic role for a conserved tyrosine and distinct S1′ recognition site. Taken together, these results identify REP34 as an active carboxypeptidase, implicate the enzyme as a potential key F. tularensis effector protein, and may help elucidate a mechanistic understanding of F. tularensis infection of phagocytic cells.

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Acid Resistance in Francisella tularensis

2014

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Francisella tularensis, the etiologic agent of tularemia, can survive under acidic conditions. Tularemia can be acquired by several routes, including by ingestion of contaminated food or water. While acid resistance is usually associated with a low oral infective dose (ID), the ID for gastrointestinal illness is quite high. In this study, four strains of F. tularensis ssp. tularensis (type A) and four strains of F. tularensis ssp. holarctica (type B) were examined for innate acid resistance and the ability to survive in synthetic gastric fluid (SGF) under in vitro conditions similar to passage through the human stomach. Survival for all strains was significantly less in pH 2.5 SGF than in pH 2.5 phosphate-buffered saline and pH 4.0 SGF. Attenuated strains were consistently less resistant. Type B strains are most often associated with waterborne outbreaks and were examined after storage in natural water. Low-nutrient preadaptation resulted in increased resistance. Although F. tularensis can persist under certain acidic conditions, it is sensitive to conditions replicating the fasting human stomach. This may help explain the high ID required for gastrointestinal infections.

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Francisella tularensisType A Strains Cause the Rapid Encystment ofAcanthamoeba castellaniiand Survive in Amoebal Cysts for Three Weeks Postinfection

Cited by 94 publications

References 52 publications

Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

Structure and Function of REP34 Implicates Carboxypeptidase Activity in Francisella tularensis Host Cell Invasion

Acid Resistance in Francisella tularensis

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